Defence in a game good, leading to victory finally (7)
I believe the answer is:
apology
'defence' is the definition.
(apology is a kind of defence)
'a game good leading to victory finally' is the wordplay.
'game' becomes 'polo' (polo is a kind of game**).
'good' becomes 'g' (abbreviation).
'leading to' means one lot of letters go next to another (some letters go before or lead others).
'finally' indicates one should take the final letters.
The last letter of 'victory' is 'y'.
'a'+'polo'+'g'+'y'='APOLOGY'
'in' is the link.
(Other definitions for apology that I've seen before include "Explanation for a fault" , "Regrets < poor" , "Expression of regret for offence given" , "A poor example" , "defence" .)